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| 2. |
- Carlsson, Anna K, 1966, et al.
(författare)
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High-resolution photoemission from a tunable quantum well: Cu(111)/Na
- 1997
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 56:3, s. 1593 - 1600
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution photoemission (ΔE=5 meV) at a low photon energy (3.82 eV) is used to probe discrete quantum-well-type subband states near, below, and above EF for Cu(111) covered with 2 ML or less of Na. A subband characteristic of the monolayer range shifts gradually to lower energy as the coverage is increased, extending below the Fermi level for coverages above 0.85 ML. Combined with previous observations of shifts for filled and empty states the present results show that the Na monolayer has continuously tunable quantum-well state energies. Beyond the monolayer range quantum-well states characteristic of both one and two atomic layers are observed, indicating growth of the second layer via monolayer high islands. A small downshift, by 25 meV, with increasing coverage in the second layer is ascribed to an increase of the island size. Lorentzian photoemission line shapes are observed for well-ordered samples. The linewidth varies linearly with temprature in the probed range (130–295 K) and this is ascribed to the phonon contribution to the width. Structural disorder leads to an asymmetric line, which is Lorentzian on the steeper, low-kinetic-energy side.
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| 3. |
- Carlsson, Anna K, 1966, et al.
(författare)
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Observation of structure changes for Li/Cu(111) by photoemission from Li core and quantum-well states
- 1998
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 57:20, s. 13192 - 13198
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Tidskriftsartikel (refereegranskat)abstract
- Via photoemission from discrete quantum-well valence states and the Li 1s core level, three different types of atom rearrangements are observed for Cu(111)/Li. In the monolayer coverage range gradual energy shifts for the core-level as well as a quantum-well state reflect a gradual lateral compression of the Li overlayer as more atoms are adsorbed. The onset of Li substitution and formation of a (2×2) structure when, at RT, monolayer Li coverage is exceeded, is monitored via the disappearance and appearance of quantum-well states characteristic of the adsorbed full monolayer of Li and the part substitutional (2×2) structure, respectively. A splitting of the Li 1s emission peak into a doublet reflects the two different Li sites characteristic of the (2×2) phase. A small energy shift of the quantum-well state (25 meV) indicates that, if it is cooled (170 K), the substitutional structure is unstable with respect to Li adsorption.
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| 4. |
- Carlsson, Anna K, 1966, et al.
(författare)
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Oscillatory photoemission cross section for alkali monolayer quantum well states
- 1996
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 352-354, s. 656-659
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Tidskriftsartikel (refereegranskat)abstract
- A strong oscillatory photon energy dependence, observed in the photon energy range between 5 and 26 eV, for the intensity of photoemission peaks due to quantum well states in Na and Cs monolayers on Cu(111) is ascribed to interference between the contributions to the outgoing photoelectron wave from the two tails of the quantum well state.
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| 5. |
- Carlsson, Anna K, 1966, et al.
(författare)
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Oscillatory photoemission cross section for simple-metal quantum wells
- 1995
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 52:15, s. 11144 - 11146
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Tidskriftsartikel (refereegranskat)abstract
- A strong, oscillatory photon energy dependence is observed for the intensity of photoemission peaks due to quantum-well states in Na overlayers on Cu(111). The measurements are made at low photon energies (hν
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| 6. |
- Carlsson, Anna K, 1966, et al.
(författare)
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Shifts and widths of metal-overlayer quantum-well states near EF observed by photoemission
- 1994
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 50:12, s. 8926 - 8929
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectron energy spectra reveal discrete valence-electron states in the range 0–220 meV above EF for 1–3 atomic layers of Na on Cu(111). Apart from a stepwise dependence on the number of atomic Na layers the energy of the quantum-well states depends in a gradual manner on how full the layer is. The states are as well defined in energy as comparable surface states producing peak widths (50–90 meV), which depend on temperature and coverage.
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| 7. |
- Carlsson, Anna K, 1966, et al.
(författare)
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Structure changes for Cu(111)/Li observed via discrete quantum well states
- 1997
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Ingår i: Surface Review and Letters. - 0218-625X. ; 4:6, s. 1233-1237
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Tidskriftsartikel (refereegranskat)abstract
- Via photoemission in the near UV from discrete quantum well states, four different types of atom rearrangements are observed for Cu(111)/Li. In the monolayer range a gradual energy shift reflects a gradual compression of the Li layer as more atoms are adsorbed. The onset of Li substitution and formation of a (2×2) structure when, at RT, monolayer Li coverage is exceeded is monitored via the appearance of a quantum well state characteristic of the new phase. A small energy shift indicates that, if it is cooled (170 K), the new structure is unstable with respect to Li adsorption. Finally, an energy downshift with increasing coverage observed for a state characteristic of 2 ML Li is ascribed to an increasing area for one-atomic-layer-high islands formed by Li atoms on top of the first full layer.
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| 8. |
- Carlsson, Anna K, 1966, et al.
(författare)
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Valence-Electron Resonances in Alkali-Metal Overlayers Observed via Photoemission Line-Shape Changes
- 1996
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 77:2, s. 346 - 349
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Tidskriftsartikel (refereegranskat)abstract
- Valence-electron resonances for Na overlayers on Ag(111) and Cu(111) are observed by photoemission via line-shape changes for the substrate s,p-band emission in a narrow range of photon energies. The effect is ascribed to interfering contributions to the photoelectron wave from the substrate and the vacuum barrier.
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| 9. |
- Lindgren, Stig-Åke, 1950, et al.
(författare)
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Coverage-dependent frequency for Li-atom vibrations on Cu(111)
- 1996
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 54:15, s. 10912 - 10916
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Tidskriftsartikel (refereegranskat)abstract
- Electron-energy-loss spectra recorded for monolayer amounts of Li adsorbed on Cu(111) show a loss peak associated with Li vibrations perpendicular to the substrate. The loss energy shifts from 38 meV at low coverage to 43 meV at 0.3 ML and remains constant for coverages between 0.3 and 0.5 ML. The loss intensity passes a maximum at a Li coverage of 0.15 ML and gradually decreases such that it is difficult to resolve a loss peak at coverages above 0.5 ML. The high loss energy indicates that the adatom resides on the surfaces rather than in substitutional sites. The frequency shift is much too large to be explained by dipole-dipole interactions. The above results are obtained with the evaporation source loaded with the natural Li isotope mixture (92.6% 7Li, 7.4% 6Li). Measurements with 6Li show that the increase of the vibration frequency with increasing coverage is not an isotope effect.
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| 10. |
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